An autonomous system (AS), also sometimes referred to as a routing domain, is a network having a single defined Internet routing policy. The Internet may be described as a network-of-networks, that is, a network of ASes linked with one another via an exterior gateway protocol (EGP). The current EGP of the Internet is the Border Gateway Protocol version 4 (BGPv4). ASes of the Internet for the most part share stable, pair-wise interfaces. These interfaces usually occur across wire-based network infrastructures. A mobile ad hoc network (MANET) is an autonomous system of primarily mobile nodes, e.g., mobile routers, connected primarily by wireless links. In contrast to most other autonomous systems, MANETs can be extremely flexible and are often characterized by a significant amount of mobility and geographical movement.
Because MANET nodes are mobile, however, a topology of a MANET network nodes may change quickly and unpredictably. Connectivity may be intermittent between MANET nodes, and wireless links can create the appearance of rapid topology changes through signal intermittence, even if no movement is actually occurring. Rapid topology changes often detrimentally impact convergence of routing protocols, making these protocols less reliable. BGPv4 is designed to operate within a context of providing a stable, pair-wise interface between peer nodes in different ASes. This approach can break down when a pair-wise interface peer in one AS moves out of transmission range of its peer in another AS. BGPv4 can also break down when one peer dynamically establishes a new pair-wise relationship with a new peer that comes in range in the other AS. Thus, BGPv4 is not well-suited to support highly mobile environments.
The Internet protocol (IP) currently supports a hierarchical topology system according to which network interfaces of nodes are connected into subnetworks and subnetworks are connected into networks (ASes). Subnetworks may be connected into ASes by means of interior gateway protocols such as Open Shortest Path First (OSPF) and/or Intermediate System-Intermediate System (IS-IS). As previously mentioned, ASes may be connected via EGP protocols into the Internet.
ASes of very large entities often are limited in size because of IP scaling properties of IGP protocols. A very large entity network may be physically realized as a plurality of ASes linked together by EGP protocols, even though the ASes share a common security and quality-of-service (QoS) policy and common administrative and business attributes. Because EGP protocols provide only pair-wise relationships, segmenting a large entity network into a series of ASes connected by EGP generally constrains the flexibility of the network design and can create bottlenecks within the network communication paths.